Dr. Robert Tremblay
Veterinarian
This could be running the risk of having too much on selective dry cow therapy (SDCT) but there seems to be lots of new information. The latest is also from the Netherlands. It has some findings that would be useful for Canadian dairies too.
All the dry cow therapy treatments available in Canada only claim to cure mastitis in cows treated at dry off. But when researchers investigate the effectiveness of dry treatments, they usually look to see how well dry cow treatments prevent cows from getting a new mastitis infec- tion during the dry period too. Selective dry cow treatment is designed to avoid treating cows that don’t have clinical or subclinical mastitis at dry o and to avoid using antibiotics to prevent disease. Pro- tecting the udder from new infections is really prevention.
The risk of a cow getting a new mastitis infection during the dry period is likely influenced by how cows are dried off and how they are managed during the dry period. The risk of a new infection is going to be different on different farms.
When SDCT was mandated in the Netherlands, many feared that more cows would freshen with a new case of mastitis as a result. As I laid out last month, that did not happen although there were other changes that happened at the same time, not just the switch to SDCT.
In this 2018 Dutch study, researchers looked at what management practices farmers believed were important to udder health during the dry period. Almost 700 farmers shared their experiences through an on-line survey. The researchers also had access to the udder health information for those farmer’s herds so they could look at the relationship between farm practices and procedures and the risk of new mastitis infections during the dry period. A cow was considered to have become infected during the dry period if her somatic cell count was < 250,000/ml on the last test before dry off but over 250,000/ml on the first test if the next lactation.
The average herd size was 112 cows with about a third of the herds milking fewer than 80 cows. Just about a quarter of the herds used milking robots. Almost all the farms housed dry cows in free stalls with either mattresses or deep bedding rather than in group housing.
During the study, 16% of cows on the study farms developed a new infection during the dry period.
The dairy farmers in the survey felt that lowering milk production was the most important management practice prior to dry off. Most herd managers did that by changing the milking interval although some also changed feeding too.
The upper limit of the average production in the herds at dry-off was 13.5 kg. Farmers also reported that they used more than just SCC data when they made dry-off treatment decisions. They looked at other factors that could increase the risk that a cow might become infected during the dry period to decide whether to use an intramammary antibiotic at dry-off. The increased risks were leaking milk, high milk production at dry-off, being an older cow or having good milk letdown.
Amongst the management practices that were associated with a low risk of cows developing new infections during the dry period, using teat dipping or teat spraying after dry-o was most important. Understanding the need for good hygiene at dry-off was also important.
Some people might argue that Dutch dairy production is different from Canadian production. That might be true, but this survey suggests that the same factors that experts believe are important in dairy herds here were important to helping prevent new infections on the farms in the Dutch survey.
Dr. Robert Tremblay is a veterinarian for Boehringer-Ingelheim and lives near Guelph.
